I. Field
The present disclosure relates generally to communication, and more specifically to techniques for generating weights for transmit diversity in a wireless communication system.
II. Background
In a wireless communication system, a transmitter modulates a radio frequency (RF) carrier signal with data and generates an RF modulated signal that is more suitable for transmission over a wireless channel. The transmitter then transmits the RF modulated signal via the wireless channel to a receiver. The transmitted signal may reach the receiver via a number of propagation paths. The characteristics of the propagation paths may vary over time due to various factors such as fading, multipath, interference, and so on. Consequently, the transmitted signal may experience different channel conditions and may be received with different amplitudes and phases over time.
Transmit diversity may be used to provide diversity against deleterious path effects and improve reliability. Transmit diversity utilizes multiple transmit antennas for data transmission. A propagation channel is formed between each transmit antenna and the receive antenna. If the propagation channels for different transmit antennas are linearly independent, which is generally true to at least an extent, then diversity increases and the likelihood of correctly receiving a data transmission improves as the number of transmit antennas increases.
With transmit diversity, data is redundantly sent on multiple RF modulated signals transmitted from the multiple transmit antennas to the receive antenna. The RF modulated signals typically experience different channel conditions and may be associated with different complex channel gains. Consequently, these signals may arrive at the receive antenna with different amplitudes and phases and may add constructively or destructively. A control loop may be maintained to determine the proper weights to apply to the RF modulated signals at the transmitter such that these signals add constructively at the receiver. A challenge is then how to generate the weights such that good performance can be achieved.
There is therefore a need in the art for techniques to generate weights for transmit diversity.